The present application is a U.S. non-provisional application based upon and claiming priority from Japanese Application No. HEI 10-370370, which is hereby incorporated by reference.
The present invention concerns a method for manufacturing aromatic carbonates, and specifically concerns a method for manufacturing aromatic carbonates which makes it possible to manufacture aromatic carbonates efficiently and inexpensively from dialkyl carbonates and aromatic hydroxy compounds.
Diphenyl carbonate (DPC) is a compound that is industrially useful as a raw material for the manufacture of polycarbonates, etc. Accordingly, the manufacture of aromatic carbonates with good productivity has great industrial value.
It has long been known that diaryl carbonates such as diphenyl carbonate, etc., can be obtained by reacting dialkyl carbonates with aromatic hydroxy compounds.
For example, when dimethyl carbonate and phenol are reacted, methylphenyl carbonate, diphenyl carbonate or a mixture of both compounds is obtained as shown below. ##STR1##
However, the above reactions are all equilibrium reactions, and the rates of these reactions are slow.
Various types of catalysts, which for example increase the reaction rate, have been proposed as means of solving such a problem.
Furthermore, attempts have also been made to separate alcohols such as methyl alcohol, etc., produced as by-products in the reaction from the raw materials, product or solvent, and to distill such alcohols away so that the reaction is caused to proceed to the product system side, and the use of reactors with attached distillation columns is also known.
Furthermore, a method for the continuous manufacture of aromatic carbonates in which a continuous multi-stage distillation column is used, and alcohols, etc., produced as by-products by the reaction are continuously removed from the system by distillation, so that the reaction product can be continuously led out of the system while causing the reaction to proceed to the product system side, has been proposed in Japanese Laid-Open Patent Application (Kokai) No. Hei 3-291257.
In the case of such a reaction, it is known that alkyl aromatic ethers are produced as by-products in addition to the aromatic carbonate constituting the intended product. For example, it is known that anisole is produced as a by-product according to the following formula when dimethyl carbonate is reacted with phenol. ##STR2##
It is thought that this anisole is produced as a result of a de-carbonic acid reaction of methylphenyl carbonate with the reaction product of dimethyl carbonate and phenol. If the reaction of dimethyl carbonate and phenol is performed at a high temperature in order to increase the production efficiency of the aromatic carbonate, the production rate of anisole increases.
Accordingly, in Japanese Laid-Open Patent Application (Kokai) No. Hei 9-165357, the present inventors discovered that aromatic carbonates can be manufactured with good productivity and with little production of alkyl aromatic ethers as by-products by reacting dialkyl carbonates and aromatic polyhydric hydroxy compounds under specified conditions, and such a manufacturing process was proposed.
In cases where polycarbonates are manufactured by means of a melt polycondensation reaction using such aromatic hydroxy compounds, aromatic hydroxy compounds are also produced as by-products. If aromatic carbonates are manufactured by reusing such by-product aromatic hydroxy compounds as raw materials, the manufacturing cost of such aromatic carbonates can be lowered, so that the inexpensive manufacture of aromatic carbonates may be expected.
In Japanese Laid-Open Patent Application (Kokai) No. 9-165443, the present inventors proposed the inexpensive manufacture of polycarbonates by recycling and reusing aromatic hydroxy compounds produced as by-products during polycarbonate manufacture in a diaryl carbonate manufacturing process.
However, in this method as well, purification of the by-product aromatic hydroxy compounds was necessary, so that the results were not always satisfactory.
When the present inventors conducted research in light of the above-mentioned prior art, the inventors discovered that even if crude aromatic hydroxy compounds containing aromatic polyhydric hydroxy compounds are used, aromatic carbonates can be manufactured by using a Lewis acid containing titanium atoms as a catalyst, and setting the molar ratio of the catalyst to aromatic polyhydric hydroxy compounds contained as impurities at a specified ratio. This discovery led to the perfection of the present invention.